The loading of unmanned barges is not regulated in Canada. The amount of cargo carried by any unmanned barge between Canadian ports on the west coast is established by practice. The problem is augmented by the lack of the explicit authority or sufficient training, or both, on the part of some tug skippers, which would be needed to determine the limit of the load on the barge. The statement by the crew that the barge B-525 was carrying the second largest recorded load is based on their visual assessment. The vehicles, especially the back-hoe and the bulldozers, may be fitted with attachments, such as grabs and blades, of various sizes. Thus their weights may differ from the nominal weights provided by the manufacturer. The snow covering the vehicles also added some weight. It could be that the total load on the B-525 on 5November 1996 was the largest ever carried on this barge and produced a capsizing potential well beyond the barge's margin of righting ability. Capsizing occurs when a vessel loses transverse stability due to an individual cause or a combination of contributory causes. In the case of an intact and initially stable vessel, capsizing is often initiated by the transverse movement of a weight already onboard or the effect of an external force greater than the righting ability of the vessel at the time. Those attending the loading operation onboard the tug acknowledged, and further post-occurrence inspections and inquiries confirmed, that the barge was upright when loading was completed. However the barge started to heel immediately after the tug backed it off the beach. It is conceivable that the square bow of the barge was resting on the bottom during the loading operation thus preventing it from listing until it was fully afloat. It is impossible to assess the barge's transverse stability without proper documentation, exact weights and departure draughts. However, from the reported sequence of events, it may be derived that the initial GM of the barge was oscillating about zero and, with a freeboard of only about 2 inches (5.1cm), the range of positive righting arm values was, at best, very small. An initial small heeling moment could induce the barge to heel to such a degree that the positive righting arm vanished. The subsequent shift of the cargo and the resultant increase in heeling moment caused the heeling to continue and accelerate, until transverse stability was suddenly overcome. After the repositioning of the vehicles the barge seemed to be upright. Although the horizontal transfer of the cargo eliminated the list, it did not improve the barge's transverse stability. The small moment, sufficient to overcome the initial righting ability, if there was any, could have been generated by the centrifugal effect of the turning barge, or by the weather, or by the combination of both. The weather and handling of the tug and barge were acceptable and should not normally have caused capsizing. However the excessive amount of cargo loaded on barge's deck made it susceptible to any, even small, heeling moments, that could be induced by the wind or the turning effect.Analysis The loading of unmanned barges is not regulated in Canada. The amount of cargo carried by any unmanned barge between Canadian ports on the west coast is established by practice. The problem is augmented by the lack of the explicit authority or sufficient training, or both, on the part of some tug skippers, which would be needed to determine the limit of the load on the barge. The statement by the crew that the barge B-525 was carrying the second largest recorded load is based on their visual assessment. The vehicles, especially the back-hoe and the bulldozers, may be fitted with attachments, such as grabs and blades, of various sizes. Thus their weights may differ from the nominal weights provided by the manufacturer. The snow covering the vehicles also added some weight. It could be that the total load on the B-525 on 5November 1996 was the largest ever carried on this barge and produced a capsizing potential well beyond the barge's margin of righting ability. Capsizing occurs when a vessel loses transverse stability due to an individual cause or a combination of contributory causes. In the case of an intact and initially stable vessel, capsizing is often initiated by the transverse movement of a weight already onboard or the effect of an external force greater than the righting ability of the vessel at the time. Those attending the loading operation onboard the tug acknowledged, and further post-occurrence inspections and inquiries confirmed, that the barge was upright when loading was completed. However the barge started to heel immediately after the tug backed it off the beach. It is conceivable that the square bow of the barge was resting on the bottom during the loading operation thus preventing it from listing until it was fully afloat. It is impossible to assess the barge's transverse stability without proper documentation, exact weights and departure draughts. However, from the reported sequence of events, it may be derived that the initial GM of the barge was oscillating about zero and, with a freeboard of only about 2 inches (5.1cm), the range of positive righting arm values was, at best, very small. An initial small heeling moment could induce the barge to heel to such a degree that the positive righting arm vanished. The subsequent shift of the cargo and the resultant increase in heeling moment caused the heeling to continue and accelerate, until transverse stability was suddenly overcome. After the repositioning of the vehicles the barge seemed to be upright. Although the horizontal transfer of the cargo eliminated the list, it did not improve the barge's transverse stability. The small moment, sufficient to overcome the initial righting ability, if there was any, could have been generated by the centrifugal effect of the turning barge, or by the weather, or by the combination of both. The weather and handling of the tug and barge were acceptable and should not normally have caused capsizing. However the excessive amount of cargo loaded on barge's deck made it susceptible to any, even small, heeling moments, that could be induced by the wind or the turning effect. Neither the tug nor the skipper were certificated by the Marine Safety Branch of Transport Canada. The barge was not fitted with draught marks, documentation or any other means of establishing the safe load and freeboard during loading operations. The deadweight of the barge on departure was such that it did not retain sufficient intact transverse stability to withstand a small initial heeling moment. All five vehicles carried on barge's deck slipped off and sank. The post accident inspection by the Marine Safety Branch of Transport Canada found the tug unfit for commercial towing or pushing and suspended its operation. No pollution of the environment was observed. A minor oil leak from the sunken vehicles dispersed without trace.Findings Neither the tug nor the skipper were certificated by the Marine Safety Branch of Transport Canada. The barge was not fitted with draught marks, documentation or any other means of establishing the safe load and freeboard during loading operations. The deadweight of the barge on departure was such that it did not retain sufficient intact transverse stability to withstand a small initial heeling moment. All five vehicles carried on barge's deck slipped off and sank. The post accident inspection by the Marine Safety Branch of Transport Canada found the tug unfit for commercial towing or pushing and suspended its operation. No pollution of the environment was observed. A minor oil leak from the sunken vehicles dispersed without trace. The barge B-525 capsized immediately after departure because its deadweight was such that it did not retain sufficient intact transverse stability to withstand a small heeling moment. The barge was heavily loaded and had it been properly measured, the established loadline would have been exceeded.Causes and Contributory Factors The barge B-525 capsized immediately after departure because its deadweight was such that it did not retain sufficient intact transverse stability to withstand a small heeling moment. The barge was heavily loaded and had it been properly measured, the established loadline would have been exceeded.